N-634J is Jensen’s HP-16, Sn 16-3. It is an HP-15 fuselage and tail feathers with HP-16, wings. It was built by Delbert Jensen. The first flight was 7/12/73. Delbert flew it a total of 23:15 with his last flight 8/3/80. His log entries mostly show Isley Field in Iowa with only one cross country trip.
The ship was purchased by Robert Leonard (my dad) and Robert Park in January of 1985 and brought to Hutchinson Kansas. At that time it suffered from significant de-bonding of the left inboard lower wing panel. The ruddervator cord was increased about 2 inches by riveting a single sheet into the trailing edge of the existing ruddervators. (The feathers started off as HP- 15 tail feathers, so this still leaves them smaller than a standard HP-16.) My brother Steve and l took turns flying the glider for the next two years. Dad got two flights in it and Robert Park got just one. I put three 5+ hour flights in it the best being a 277 mile flight from Hutchinson Kansas to Dalhart Texas
In early '87. Robert Park sold his share to Steven Leonard (my brother). At this point the ship had about 90 hours. Steve flew it in Region 10 Sports class, a fun contest at Hutchinson and the TSA lap races. At the end of '87.Steve sold his share to Robert Leonard. I resumed mooching on my Dad to fly it until 1992 when I finally bought it from him.
Up to that point I had chronic problems with the wheel brake leaking. The ship has a hydraulic drum brake. I believe the problem was that we had automotive parts in the cylinders and were working on the assumption that it should use aircraft brake fluid. I replaced the cups in the slave cylinder with automotive parts and went to automotive brake fluid. It has worked OK since then.
In
'92 I moved to Kansas City where I started flying out of East Kansas City
Airport at Grain Valley, MO. The next winter I cut the mass balances off the
ailerons (this makes them like the HP-18) bonded a thin curved aluminum strip
to the aileron and installed myIar gap seals. This seemed to improve the high
speed performance, but I never measured the change.
In Hutchinson we had a strong tow plane and a huge runway which faced into the prevailing wind. In Kansas City, I was faced with a weak tow plane and a narrow east west runway in a land of South Wind. Each takeoff the first year at Grain Valley was an experience in terror, the worst being a ground loop at fairly high speed that split the tail wheel and tore off a tip plate. At the end of '94 I decided something needed to be done to improve takeoff control. Over the winter, I converted one segment of flap to aileron and put the tail wheel on the bottom of a six inch ventral fin to reduce the angle of attack. I measured control surface deflections and found that l didn't get near as much right aileron as left. A little filing took care of this problem. With the aileron modifications the take off control went from absolutely awful to docile. Haven’t dropped a wing since. Even with 8 feet less total flap span, flap performance is sufficient. I have turned sort final at 1000 feet and still hit the middle of a 2300 foot runway.
Also in the winter of 94/95, the left wing lower surface de-bonding problem was finally repaired. With the help of my Dad the rivets were drilled out and the skin peeled off. The de-bonding was so complete that no ribs were damaged in the process. The skin was re-bonded after minimal cleaning using ProSeal (Sealpak Company, Inc. 2614 S. Hoover, Wichita, Ks 67215 Phone 316 942-6211 Ask for Proseal fuel tank sealer B-2, The number on the can I have is: CS3204 B-2, Mil-S-8802F. ) To get a good Epoxy bond takes careful preparation. The epoxy bond will not stand up to direct exposure to moisture. Schreder didn't use ProSeat for fear it would creep. Others have told me the fuel tank sealer has less strength than bubble gum. The particular stuff I used cannot be failed without destroying the aluminum it holds. It will hold up to direct exposure to moisture. It takes minimal care in surface preparation. To date, I have had no problems with my wing in the repaired area. I am working on an HP-18 and plan to build a wet wing bonded with the stuff.
The winter of 95/96 I made a fiberglass canopy frame for the center section. I did the glass lay ups on the fuselage and existing canopy frames. I used electrical tape for a parting agent, It came out OK.
The winter of 98/99 I replaced the floor in the trailer. It is an SST trailer. The wooden floor was riveted in. Getting it out took many hours. I ended up putting in a floor that was 1/8” thinner with external stiffeners. The original thickness floor would not go back in the now mangled angles. I also replaced the axle. The original was bent and scrubbed a set of tires to death about every 7500 miles.
The winter of 99/00 I cut the ventral back off and went back to stock tail wheel. I made fiberglass gear doors with a bit tighter fit than the original metal ones. I also installed double seal o-rings in struts (previously they had never held pressure).
The biggest problem I have had with the ship is the tail feather gap seals. The angles on the tail are sharper than standard for a 16 or 18. I have made two sets out of fiberglass and one from Copper Berillium. The fiberglass ones never sealed throughout the range of motion and made for high stick force in the last bit of travel. They tended to crack and straighten out over time. The Copper Berillium ones fluttered and departed the airplane in flight. Right now the tail is unsealed.
The spar carry through webs were originally made of Magnesium. They were very hard to keep from corroding and had a couple of places they were starting to pit noticeably. Finally gave in and made replacements out of .09” 2024-T3 using the originals as a guide for cutting and drilling the old one. The real trick was in bolting and riveting it back together so that the wing pins would still go in.